1. Field of the Invention
The present invention relates to an ignition apparatus and a method for igniting an internal combustion engine. In particular, the present invention and method are particularly useful in an in-cylinder direct gasoline engine, a gas engine with an accessory cell, and others.
2. Description of the Related Art
Combustion embodiments of recently practiced in-cylinder direct gasoline engines include a uniform premixed air-fuel mixture combustion with fuel injection during inlet strokes of a piston and a stratified combustion with fuel injection during compression strokes.
In the stratified combustion, it is important to send an air-fuel mixture, which is most suitable to ignite, on the periphery of spark plugs. It is known that the time from a firing of a spark plug to a fuel ignition as a start of combustion has dispersions depending on driving conditions (for example, a fuel injection timing, a valve opening-closing timing, flowing of an air-fuel mixture in a cylinder). It is described in a following explanation that a fuel ignition as a start of combustion is the ignition, and that a firing of a spark plug is the firing.
Therefore, if the duration of an inductive current, which is induced by an ignition coil at discharging spark, is determined to be longer than that of the uniform premixed air-fuel mixture combustion, it certainly makes an ignition possible and the combustion is always stable, whereby the stratified combustion is available in response to any driving condition.
However, if the spark discharge time is determined to be longer as mentioned above for obtaining the secure ignition under unstable conditions, the inductive current necessary to the spark discharge is given to the spark plugs for a certain time, irrespective of driving conditions. In certain-driving conditions, the inductive current is continuously supplied between electrode gaps of the spark plug after the ignition, whereby to accelerate an electrode wear of the spark plug by excessive spark energy and to probably shorten a life cycle of the spark plug.
It is an object to the invention to offer an ignition apparatus for internal combustion engine and a method capable of improving the life cycle of the spark plugs without spoiling the ignition capacity of the internal combustion engine.
In order to achieve the above object, an ignition apparatus for an internal combustion engine of the invention, is equipped with:
at least one spark plug operable to ignite a fuel mixture in at least one cylinder of an internal combustion engine;
an ignition coil including at least one primary coil and at least one secondary coil operable to generate a spark discharge voltage to be supplied to the at least one spark plug;
a spark discharge voltage detecting unit operable to detect the spark discharge voltage;
an ignition detecting unit operable to detect an ignition in the at least one cylinder during a period when the ignition coil supplies the spark discharge voltage;
a first ignition control unit operable to control a current supplied to the at least one primary coil for generating the spark discharge voltage in the at least one secondary coil; and
a second ignition control unit operable to control the current supplied to the at least one primary coil to stop the supply of the spark discharge voltage in the at least one secondary coil, wherein said second ignition control unit stops the supply of the spark discharge voltage in the at least one secondary coil based on the detected ignition during the period when the ignition coil supplies the spark discharge voltage.
The ignition apparatus for an internal combustion according to another embodiment of the present invention may include a driving condition discriminating unit that may determine operating conditions of the internal combustion engine and supply the determined operating conditions to the ignition control unit, the spark discharge voltage detecting unit, and the ignition detecting unit. The operating conditions may include, for example, and air-fuel mixture, a lean condition, or layer air-intake conditions.
Another embodiment of the present invention may include a feature wherein the ignition detecting unit detects the ignition in the cylinder based on a predetermined high frequency component included in the spark discharge voltage. Further, the present invention allows for stopping the supply of the spark discharge voltage by providing current to the one primary coil.
In yet another embodiment of the present invention, the first ignition control unit is operable to control the supply of current to the at least one primary coil to generate the spark discharge voltage in the at least one secondary coil, and the second ignition control unit operable to interrupt the supply of the current to the at least one primary coil.
Also, the present invention allows for repeatedly supplying and interrupting the supply of the current to the at least one primary coil by the first and second ignition control units.
Further, the spark discharge voltage detecting unit of the present invention may include a coupling capacitor used in conjunction with the primary and secondary coils.
A method for controlling ignition in an internal combustion engine according to the present invention may include the steps of:
controlling a current supplied to a primary coil of an ignition coil for generating and stopping a spark discharge voltage in a secondary coil of the ignition coil;
supplying the spark discharge voltage from the ignition coil to an spark plug;
detecting the supplied spark discharge voltage;
detecting an ignition in at least one cylinder of the combustion engine in accordance with the detected spark discharge voltage during a period when the ignition coil supplies the spark discharge voltage; and
stopping the supply of the spark discharge voltage based on the detected ignition.
In a further step, the ignition may be detected based on a predetermined high frequency component included in the spark discharge voltage. In addition, the supply of the spark discharge voltage may be stopped by providing the current to the primary coil.
Therefore, according to the aforementioned embodiments, in a first aspect of the invention, for the period when the spark discharge voltage is detected by the spark discharge voltage detecting unit and when the ignition coil supplies the spark discharge voltage by the ignition detecting unit, the ignition of each cylinder is detected in accordance with the detected voltage by the spark discharge voltage detecting means when the ignition detecting unit detects the ignition by the second ignition control unit, the supply of the spark discharge voltage is stopped for the discharging period when supplying the spark discharge voltage which indicates to detect the ignition. Thereby, the ignition is detected and the supply of the spark energy is stopped, so that it is possible to prevent the supply of the excessive spark energy to the spark plug after the ignition.
Incidentally, the purpose of detecting the ignition is to detect misfires concurrently. But a detailed investigation is actually necessary for each of engines to determine a threshold value for judging the ignition or the misfire if detecting the ignition from the spark discharge voltage, and trying to judge the ignition or the misfire by a predetermined threshold value, even if it is actually the misfire, there happens 10 to 20% of the whole cases that waveforms of the spark discharge voltage indicate the ignitions owing to variations of engine characteristics or variances in environmental conditions. But, as the invention has a purpose of steadily detecting the ignition, it is not necessary to set the threshold value in such a boundary area (gray zone) where the ignition or the misfire is not always clear ordinarily, or where a judgment depends on the environmental conditions. But it is sufficient to set the threshold value for ignition detection in the boundary between the gray zone and an area (white zone) where the ignition can be certainly judged. In this case, when the waveform of the spark discharge voltage cannot distinctly judge the misfire or the ignition, the spark discharge is continued without interruption, even though it is actually the ignition. But this is a slight influence in another object of the invention reducing consumption of the plug, since 10 to 20% of the whole cases that the spark discharge is continued without interruption. It is possible thereby to avoid an error of interrupting the spark discharge by an error detection of the ignition in spite of the misfire. In the present invention, it is important for the present invention not to set the threshold value in the gray zone.
In a second aspect of the present invention, when the driving condition of the internal combustion engine is discriminated as, for example, a lean or layer air-intake condition by means of the driving condition is criminating means for discriminating driving conditions of the internal combustion engine, the control is carried out through the spark discharge voltage detecting unit, the ignition detecting unit and the second ignition control unit. Thereby, under the driving condition of lean or layer air-intake where the supply time of the spark discharge voltage by the ignition coil is longer than that of the uniform air-fuel premixture, it is possible to prevent the supply of the excessive spark energy to the spark plug after the ignition.
In a third aspect, the detection of ignition by the ignition detecting unit may be performed by detecting predetermined high frequency components included in the spark discharge voltage. Thereby, it is possible to detect the high frequency oscillation of the discharged voltage caused by disturbing a discharged spark of the spark plug through the good combustion after ignition, so that the ignition detection can be easily done.
In a fourth aspect, the stoppage of supply of the spark discharge voltage by the second ignition control unit is performed by re-supplying a primary current of the ignition coil to the primary coil. Thereby, in the secondary coil of the ignition coil, an inductive current is generated in a reversal direction to the already generating inductive current, so that it is possible to restrain an occurrence of the spark discharge voltage by the ignition coil.
In a fifth aspect, control maybe carried out for repeatedly plural times generating the spark discharge voltage to the ignition coil by means of the first ignition control unit, and the control for the repeating generations by the first ignition control unit is interrupted by means of the second ignition control unit. Thereby, the interrupting control by the second ignition control unit is performed for the first ignition control unit, so that it is possible to easily embody the stoppage of supply of the spark discharge voltage by the second ignition control unit.
In a sixth aspect, the ignition coil comprises plural coils which are provided with the ignition control unit of a plurality of coils supplying in succession and separately the spark discharge voltage in substitution for the first ignition control unit, and the stoppage of supply of the spark discharge voltage by the second ignition control unit is performed by the interruption of successive supply of the spark discharge voltage by the ignition control unit of the plural coils. Thereby, the interrupting control is performed by the second ignition control for the ignition control unit of the plural coils, so that it is possible to easily embody the stoppage of the spark discharge voltage by the second ignition control unit.
In a seventh aspect, in the ignition apparatus for internal combustion engine, the stoppage of supply of the spark discharge voltage by the second ignition control unit is performed together with re-supply of the primary current to the primary coil of the ignition coil. Thereby, although during the period of repeating supply of the spark discharge voltage by the first ignition control unit in the first ignition control unit, or during the period of supplying the spark discharge voltage by the coil in the plural coil ignition control unit, an inductive current is generated in a reversal direction to the already generating inductive current in the ignition coil or in the secondary coil of the coil, so that it is possible to restrain occurrence of the spark discharge voltage by the ignition coil et al.
In an eighth aspect, the spark discharge voltage detecting unit may be equipped with a coupling capacitor for a primary circuit of the ignition coil or a secondary coil circuit of the ignition coil. By means of such a comparatively simple circuit composition of connecting a capacitor in series to the primary coil circuit or the secondary coil circuit, it is possible to take out an objective predetermined high frequency components, while removing direct current components.